Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$200.54	13.276%	$227.1637	$227.16	$227.15	$227.20
Purchase #2	$124.64	11.218%	$138.6221	$138.62	$138.60	$138.60
Purchase #3	$62.61	5.487%	$66.0454	$66.05	$66.05	$66.00
Purchase #4	$30.78	12.601%	$34.6586	$34.66	$34.65	$34.70
Purchase #5	$92.74	7.715%	$99.8949	$99.89	$99.90	$99.90
Purchase #6	$148.73	4.105%	$154.8354	$154.84	$154.85	$154.80
Purchase #7	$70.50	11.645%	$78.7097	$78.71	$78.70	$78.70
7 purchase totals =	$730.54		$799.9298	$799.93	$799.90	$799.90